This section provides background information related to the present disclosure which is not necessarily prior art.
Hydraulically operated clutches generally include a piston which applies force to the clutch system to engage a plurality of clutch plates. In order for the clutch plates to reach maximum separation for low drag torque, the piston must retract a considerable distance from the point of engagement. Typically, for the piston to move from the fully retracted position to engage the clutch plates quickly, a high flow of hydraulic fluid to the piston is required during this initial actuation. As the clutch plates are not engaged during this initial movement of the piston, the fluid can be provided at a lower pressure. Once the clutch plates begin to engage, the piston has less distance to travel before the clutch is fully engaged, thus the high flow rate is no longer needed. Instead, a higher pressure is required to force the clutch plates into complete engagement.
Typically, the pressure developed by a fixed displacement hydraulic pump (e.g. a gerotor pump) is directly related to the pump's input torque, and inversely related to the pump's fluid displacement, while the flow rate is directly related to the pump's fluid displacement and rotational speed. As a result, it can be difficult to satisfy requirements for low power consumption, high flow rate, and high pressure, while simultaneously maintaining simplicity, low cost, and robustness of a fixed displacement pump.